Non-inductive electrical resistor



Aug. 16, 1966 R. L. DAVIS 3,267,405

NON-'INDUCTIVE ELECTRICAL RESISTOR Filed May 1, 1964 I? Y Richard L.Davis IN V EN TOR.

ATTORNEY United States Patent represented by the United States AtomicEnergy Commission Filed May 1, 1964, Ser. No. 364,341 3 Claims. (Cl.338-63) This invention relates to electrical resistors, particularly tonon-inductive electrical resistors.

In high voltage, high frequency electronic circuits, especially in pulseapplications such as radar, the design and operation of these circuitsis greatly affected by unknown reactance in' the circuit componentsthemselves or in unwanted coupling between components. A large amount oftime andfmoney has been expended to develop components that display inthese applications the particular electrical function for which it wasdesigned. Under ideal circumstances, a resistor should essentiallyprovide only resistance to the circuit, a capacitor only capacitance andan inductor only inductance.

This has been a problem in the resistor field and particularly in 'lowresistance resistors. Previously known low resistance resistors havedisplayed in high frequency and pulse applications some form ofdeleterious reactance or coupling with other components.

It is therefore an object of this invention to provide a non-inductiveresistor which is both simple and inexpensive to produce and flexible inusage.

It is a further object of this invention to provide a resistor which hasno residual self inductance or mutual inductance.

It is a further object to provide a resistor which is nonreactive athigh frequencies.

Various other objects and advantages will appear from the followingdescription of one embodiment of the invention, and {the most novelfeatures will be particularly pointed out hereinafter in connection withthe appended claims.

This invention contemplates utilizing insulated resistive material inthe form of a mobius surface with electrical leads attacheddiametrically opposite each other to the resistive material as anon-inductive resistor.

For a better understanding of the invention, reference may be had to theaccompanying drawings in which:

FIGURE 1 is a perspective View of one embodiment of this invention,

FIGURE 2 is a cross-sectional view of the mobius strip showing thelocation of the resistor, insulator and electrical leads and FIGURE 3 isa cutaway view of a section of a resistor which embodies this invention.

In the embodiment of the invention illustrated in FIG. 1 and FIG. 2,non-inductive resistor 1 comprises nonconductive ribbon 2 of aninsulative material such as Mylar (polyethylene terephthalate) on bothsides of which resistive ribbons 3 and 4 have been applied. Resistiveribbons 3 and 4 can be made of a resistive material such as Tophet A (80Ni, 20 Cr) or for very low resistances, aluminum. The combined ribbons,2, 3 and 4 are then twisted as shown at point 5 and resistive ribbon 3connected to resistive ribbon 4 such as by soldering so as to form amobius strip. Resistive ribbons 3 and 4, when connected form a singlemobius surface. Electrical leads 6 and 7 are then attached such as bysoldering to diametrically opposite points 8 and 9 of resistive ribbons3 and 4 to complete the resistor.

It is understood that the resistive ribbons 3 and 4 may be replaced byresistive wire such as Manganin (84 Cu, 12 Mn, 4 Ni) bifilar wirewherein the insulation normally providedwould replace non-conductiveribbon 2. By bifilar wire, it is meant two parallel strands of wirecovered by and separated by the same insulator. The spacing between thewires provided by the insulation should be maintained when therespective wires are connected together to form the mobius strip so asto have minimum reactance in the resistor.

In operation, a high frequency electrical current inserted acrosselectrical leads 6 and 7 will travel in opposite directions between theleads through resistive ribbons 3 and 4. The electromagnetic fieldsgenerated by these currents thereby cancel each other resulting in anessentially non-inductive, non-reactive resistor as shown in Table I.

TABLE I Conductor Resistance Reactance (200 kc.) Resistive (ohms)Material Ribbon 12.7 0.0305 microhenries Tophet A.

Do 0.1 picotarad Do.

50.3 0.090 microhenriesnu. Manganin. Do 62 0.069 picofarad D0.

The mobius resistor listed first in Table I was pulsed at 1000 volts andhad a measured rise time of 0.1 microsecond.

It was found that the reactance and/or resistance of a resistorembodying this invention was unaffected by handling or changes in form.Once the resistor is connected as described above in a mobius strip, theresistor need not be maintained in any particular form such as thatshown in FIG. 1 but can be wound around a cylindrical core or a card orfor that matter rolled in a ball providing the resistive ribbons areinsulated from each other as is well known in the art. A mobius stripresistor was wound on a cylindrical core without any effect to itsoperation thereby enabling compact packaging of the resistor.

Further, as shown in FIG. 3, two sets of resistive ribbons 10 and 11 and12 and 13 respectively were applied side by side on the samenon-conductive ribbon 14 with about a inch spacing and the combined unitconnected as described with respect to FIG. 1 so as to form two mobiusstrip resistors using ribbons 10 and 11 as one resistor and ribbons 12and 13 as the other resistor. In this form, it was found that neitherresistor in any way affected the operation of the other resistor. Theseresistors were then connected successively in series and in parallel andmeasurements made of the resulting resistance and reactance. It wasfound that the resultant resistance value changed in accordance with theusual series-parallel elfect without changing the time constant fromthat of a single resistor. Thus, a group of mobius strip resistors canbe arranged for most any resistance value either by series connection orparallel connection and still maintain the time constant. Since theseresistors can be wound around any form and not change the reactance, agroup of resistors can be made on the same nonconductive ribbon and thecombined resistor Wound around a common form with a comparable size topresent resistors.

It will be understood that various changes in the details, materials andarrangements of the parts, which have been herein described andillustrated in order to explain the nature of the invention may be madeby those skilled in the art within the principles and scope of theinvention as expressed in the appended claims.

What is claimed is:

1. A non-inductive electrical resistor comprising in combination, aribbon of non-conductive material having opposite surfaces defining acontinuous uniform surface in the form of a mobius strip, at least asingle uniform layer of resistive material disposed in continuous mannercircumferentially throughout and in parallel coextensivity on saidopposite surfaces, and a pair of electrical .leads connected to thelayer of resistive material at points aligned with each other onopposite surfaces of the non-conductive material.

2. The combination of claim 1 in which the resistive material comprisesa plurality of resistive layers and each layer is uniformly andcontinuously disposed throughout and in parallel coextensivity on thesaid opposite surfaces.

3. The combination of claim 2 in which each resistive layer has a pairof electrical leads connected thereto at points aligned with each otheron opposite surfaces of the non-conductive material.

4 t References Cited by the Examine UNITED STATES PATENTS Tarbox 336 206x 10 RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner.

1. A NON-INDUCTIVE ELECTRICAL RESISTOR COMPRISING IN COMBINATION, ARIBBON OF NON-CONDUCTIVE MATERIAL HAVING OPPOSITE SURFACES DEFINING ACONTINUOUS UNIFORM SURFACE IN THE FORM OF A MOBIUS STRIP, AT LEAST ASINGLE UNIFORM LAYER OF RESISTIVE MATERIAL DISPOSED IN CONTINUOUS MANNERCIRCUMFERENTIALLY THROUGHOUT AND INPARALLEL COEXTENSIVITY ON SAIDOPPOSITE SURFACES, AND A PAIR OF ELECTRICAL LEADS